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Tempo Charge Example

Demonstrates the one-time payment flow using a TIP-20 token transfer on the Tempo testnet (Moderato, chainID=42431).

How It Works

  1. Client sends GET /api/report — no credentials.
  2. Server responds 402 Payment Required + WWW-Authenticate challenge.
  3. Client builds and signs a TIP-20 transfer transaction off-chain.
  4. Client retries with Authorization: Payment <credential>.
  5. Server broadcasts the transaction, waits for confirmation, verifies the Transfer event.
  6. Server responds 200 OK + report JSON + Payment-Receipt header.

Prerequisites

  • Go 1.25+
  • A funded Tempo testnet wallet (alphaUSD balance ≥ 0.10)
  • The recipient address to receive payments

Setup

Server .env

Create examples/tempo/charge/server/.env:

MPP_SECRET_KEY=your-secret-key-here
RECIPIENT_ADDRESS=0xYourRecipientAddressHere
ADDR=:8087
Variable Required Description
RECIPIENT_ADDRESS Yes Address that receives the alphaUSD payment
MPP_SECRET_KEY No HMAC key for challenge signing (default: insecure demo key)
ADDR No Listen address (default: :8087)

Client .env

Create examples/tempo/charge/client/.env:

CLIENT_PRIVATE_KEY=0xYourPrivateKeyHere
SERVER_URL=http://localhost:8087
Variable Required Description
CLIENT_PRIVATE_KEY Yes 0x-prefixed private key of the paying wallet
SERVER_URL No Charge server URL (default: http://localhost:8087)

Running

Start the Server

go run ./examples/tempo/charge/server

Or with inline env vars:

RECIPIENT_ADDRESS=0xYourAddress MPP_SECRET_KEY=my-secret go run ./examples/tempo/charge/server

Run the Client

In a separate terminal:

go run ./examples/tempo/charge/client

Or with inline env vars:

CLIENT_PRIVATE_KEY=0xYourPrivateKey go run ./examples/tempo/charge/client

Example Output

Server

The server logs each step of the payment flow — you can see the unauthenticated request, the 402 challenge, the authenticated retry, and the 200 response:

Server output

Client

The client logs each step of the charge flow — challenge received, transaction built, submitted, and receipt obtained:

Client output

Endpoints

Method Path Auth Description
GET /api/health None Free health check
GET /api/report Payment One-time charge: 0.10 alphaUSD

Charge Amount

The server charges 100,000 base units = 0.10 alphaUSD (6 decimals).

Change the amount in examples/tempo/charge/server/main.go:

result := srv.Handle(r, chargeMethod, map[string]any{
    "currency":    tempo.TokenAlphaUSD,
    "amount":      "100000", // 0.10 alphaUSD (6 decimals)
    "description": "Tempo report — 0.10 alphaUSD",
})